I don't think the filehandle you are passing to rls() is valid. The cpan page for the FileHandle module provides examples that show you have to provide a filename for it to open.

    use FileHandle;

    $fh = FileHandle->new;
    if ($fh->open("< file")) {
        print <$fh>;
        $fh->close;
    }

    $fh = FileHandle->new("> FOO");
    if (defined $fh) {
        print $fh "bar\n";
        $fh->close;
    }
[download]

You need a filehandle for output so use the second version.

Update: from the documentation for Net::FTP::Recursive:

All of the methods should return false ('') if they are successful, and a true value if unsuccessful.

The rls method will write the filenames into the filehandle. The code you showed expects the files to be returned as an array.